Master cylinder for hydraulic brake systems



Maldl 26 1940. G. VAN vEsTRAu-r, ET Al. 2,194,816

MASTER CYLINDER FOR HYDRAULIC BRAKE SYSTEMS Filed Sept. 18, 1935 kw kwwm Y www wmmmw Gag?? Patented Mar. 26, 1940 l UNITED STATES PATENT OFFICE i MASTER- CYLINDER FOB HYDRAULIC BRAKE SYSTEMS Geoffrey Van Vestraut and Frank Gordon Parnell, London, England, assignors to Automotive Products Company Limited, London, England Application September 18, 1935, Serial No. 41,162 In Great Britain March 21, 1935 1 Claim. (Cl. 6054.6)

This invention relates to controlling systems actuated -by hydraulic pressure, such-for example as are'used in conjunction with vehicle brakes, aircraft controls and hydraulic controlling mech- 5 anism generally.

It is the object of the present invention to provide an improved construction of tandem master cylinder unit of the known general vform con. sisting of acylinder barrel the working space within which is bounded by an externally actuated master piston and is dividedinto 'a plurality of separate compartments by one or more floating pistons, said compartments being fed with liquid from a supply reservoir and being each arranged to deliver said liquid under pressure to one of a number of independent hydraulic systems. In operation, the `pressure created in the rst compartment by movement of the master piston is not only transmitted to the system connectedwith said compartment but also acts upon the rst of the iioating pistons and thus creates pressure in the second compartmenmand so on, if there is more than one iioating piston. It will be appreciated that in the event of a leakage developing in the system connected with any one of the compartments*v it will no longer be possible to create the normal pressure in any of the compartments owing to the equalization of pressure which takes place, and it is this diculty which 80 the present invention sets out to avoid.

In the improved arrangement the movement of the floating piston within the cylinder barrel is positively limited by the co-engagement of rigid abutments upon the master piston, uponthe v floating piston or-pistons and upon the head por-I ytion of the cylinder barrel, whereby the axial approach of the members forming the end walls of each individual working space is limited so as not to exceed a predetermineddistance. Thus,

- the axial projections carried by the oatingand master pistons may co-operate to -limit thepermissible reduction in the volume of each 'working space, and to provide a mechanical operating bridge across any working space becoming deiicient in pressure resistance, for \example due to breakage of a pipe line and consequent lleakage vof uid. The projections are preferably removable from the pistons so as to be interchangeable for adjusting the maximum permissible displacement volume of each working space. Moreover, each oating piston preferably comprises a body greater in length than its diameter and provided at its head with a piston cup packing arranged to resisttha axial ow of linuid in only one direction, and at its tail. pa means re sisting liquid ilowin both directions, said head and tail parts preferably being arranged to iit slidably in the cylinder barrel, but the intermediate'part being cut away or otherwise reduced Yin size so as to form a passage co-operating with an inlet passage feeding one of the adjacent Working spaces. The intermediate part of the'iioating piston may, if desired, be formed with an annular groove which is engaged by a stop extending radially into the cylinder barrel forlimiting the 10 axial return movement of the iioating piston.

One embodiment of the invention is illustrated in the accompanying drawing,l which shows in sectional side elevation the preferred general ar- I rangement of a tandem master-cylinder adapted 15 forvfeeding two independent hydraulic circuits, for example the brakes onthe two rear wheels and the brakes on the two front wheels of a motor vehicle.

`A common cylinder barrel i0 forms .the vbody 20 of the master cylinder, and is fitted at one end with a head portion Il secured by means of a screw thread I2, said head portion Il being provide'd with a ldelivery valve t3 communicating with an outlet union' I4 serving one of the inde- 25 pendent hydraulic systems through a pipe l5. At the other end of the Vcylinder barrel lll` a master piston I6 is arranged to be actuated by external means (not shown) through the medium of a push rod li having a head I8, a collapsible 30 boot il being iitted to prevent the ingress of dirt andmoisture to the working parts of the master cylinder i The working space of the cylinder barrel l0 is divided into two working spaces 20 land 2t by 35 means of an intermediate iloating piston member V 22. which as will be seen comprises a body formed at its head portionwith a flange 23 which iits slidably'in the cylinder barrel i0 and is engaged by a piston cup packing 24 adapted to prevent 40 the passage o! liquid outof the working space 2i. On the other hand, during retracting movement oi/ the floating piston 22 liquid -is allowed'to pass the outside o! the cup 24, and for thispllrpose a series of holes 251s provided inthe flange 23. The intermediate part of the oating piston 22 is of reduced diameter so as to provide an annular passage 26 which normally communicateswith an inlet chamber 21 through a passage 28 in the well known manner, a breathing aperture 29 be- 50 ing also formedlin the cylinderbarrei ID just in advance of the kcup 24. At its tail portion the oating piston 22 is also formed with a radial flange 3l fitting a cylinder barrel Il, and en- :aging a piston cup packing 3| resisting the pas- 55 sage of iluid out of the working space 25 and virtually constituting a cylinder head of said space. At the same time the ow of fluid in the opposite direction, i. e. from the annular space 25 to the working Aspace 25 isprevented by a flexible packing ring 32 having an inwardly directed flange which is anchored in a groove 25 formed in thhe tail part of the floating piston 22.

The working space 25 is provided with its own delivery [valve indicated at -34, while an inlet chamber`35 with associated passages 35 and 51 are identical with the corresponding parts 21, 25 vand 29 of the working space 2|. In the arrangement shown the delivery valve 34 communicates by way of a banjo connection 38 with a pipe 39 serving the second independent system, and in the usual motor car braking system the pipe 55 is connected with the cylinders of the front wheel brakes, while the pipe I5 passes to the rcylinders of the rear wheels.

For feeding the inlet chambers 21 and 35 separate reservoirs should be used. and in the arrangement illustrated a main casing 45 is provided with a filler l and a union 42 feeding by means of a pipe 43 under gravity pressure into the inlet chamber 21. An inner reservoir 44, open at its upper part, is fitted with an independent union 45 by which it is anchored within the main casing 45, and which communicates by way of a pipe 46 with the inlet chamber 35 for feeding the working space 25. When working fluid is poured into the nlling aperture of the outer casing 45, a certain proportion normally enters the inner reservoir 44, but in any case the latter must inevitably receive fluid if thecasing 45 is filledto a level above the rim 41 of the reservoir 44.

Reverting now to the mechanical featuresof the tandem master cylinder it will be seen that two return springs 48 and 49 are provided within the working space 2| and bear upon a perforated abutment plate 55, while their other ends -en.

gage with a metal plate 5| shaped to clear the recessed portion of the cup 24, thus in effect tending to return the floating piston 22 to its retracted position as shown in the drawing. To limit this movement a stop screw 52 extends radially into the cylinder barrel I5 and thus engages behind the flange 23. In order to return the master piston I6 to its retracted position a spring 53 is provided in the working space 25, and as this spring is only equal in strength to the outer spring 48 it will be seen that the force exerted by the spring 49 is unopposed and always tends to move the floating piston 22 into its retracted position against the stop 52.

In order to limit the permissible volumetric contraction of the working space 25, the master piston i5 is tted with an axial-abutment 54 having a spigot 55 which is a. force fit into a hole bored in the end of the master piston I5. Thus the abutment 54 is fairly readily removable, and this enables the correct length of abutment to be readily fitted so as to suit the particular braking system which the working space 2,5 is required to operate. Similar abutment members 55 and 51 of suitable length are also ntted to the tail end head respectively of the oating piston 22, the end of the abutment 55 being adapted to engage with the abutment 54 when the maximum contraction of the working space 25 has taken place, while the free end of the abutment 51 is arranged to engage the plate 55 for correspondingly limiting the contraction of the working space 2|. The piston cup packings 24 and 5| are provided each with a central tubular portion 5l tightly embracing the corresponding abutment members for the purpose of preventing leakage of fluid, while a similar packing 55 associated with the master piston i5 in the normal manner issimilarly shaped to embrace the abutment 54.

In the normal operation of the master cylinder the working graces 25 and 2| are completely filled with duid-from the reservoirs 44 and 45 respectively, and when a force is applied to the pushrod I1 the master piston I5 is moved along the cylinder barrel I5 -so that the cup 59 first covers the breathing aperture 31. Thereafter, fluid pressure is built up in the working space 25 and the hydraulic system associated therewith. but this iiuid pressure also acts upon the tail end of thel floating piston 22, thus overcoming the comparatively slight pressure of the springs 45 and 45 and causing endwise movement of said piston 22. After the breathing aperture 25 has been covered by the cup 24 pressure also is built up in the 'working space 2|, thus actuating'the brakes or equivalent connected to the pipe l5. In normal use, therefore, the pressure intensities in the two working compartments 25 and 2| are approximately equal and are derived from the whole of the force exerted upon the push rod I1, although, of course, the movement of the rod I1 is divided between the two compartments 25 and 2|, thus accounting for the whole of the power absorbed by the two systems associated with said working spaces 25 and 2|, neglecting frictional losses.

Assuming now that vsevere leakage of fluid takes place in the system associated with the working space 25, due for example to breakage in one of the pipe lines, this will mean that there will be a reduced resistance to contraction in the working space 25, so that the initial movement of the push rod I1 will be largely absorbed in the working space 25, the low pressure intensity therein created being insumcient to cause much movement of the floating piston 22. After the maximum proscribed contraction has taken place, however,- in the working space 25 the abutment 54 contacts with the pipe member 55, thus applying a positive mechanical force to the floating piston 22 and enabling the requisite pressure intensity to be built'up in the working space 2|. It will be realized that this working pressure in the space 2| is practically the same as would normally be obtained for any particular force applied to the push rod 1.

It'will be seen that the same effect takes place if there is loss in pressure resistance within the working space 2|, but in this case any attempt to build up pressure in the working space 25 will only have the eect of moving the floating piston'r 22 along'y the ba'rrel until' the abutment 51 coacts with the plate 55. Thereafter-further movement of the floating piston 22 is prevented so -that subsequent progress of the push rod l1 can build up the normal pressure intensity in the working space 25.

The improved form of system is, of course. readily applicable to hydraulic controlling systems .of many kinds. such for example as those used for controlling the various components of aircraft, as well as the operating means for vehicle braking systems. The component parts may, moreover, be designed in accordance with standard practice, suitable provision beingmade for feeding the systems with liquid and permitting breathing, while it may be desirable in some cases to provide valves or other members adapted inoperative positions, a stop member-carried by l to interconnect some or' all of the individual f one of the pistons so a's to come into contact with control 4branches when a predetermined pressure distribution occurs in the system as a wlole or in a particular part thereof.

What we claim to be new is:

A tandem master cylinder unit for actuating.

a plurality of independent hydraulic .systems comprising a cylinder barrel -having a uniform bore closed at one end, an externally actuated master piston slidablein .the other end, a oating piston disposed intermediate the master piston and the closed end, coiled compression springs disposed o'n each side of the iioating piston and acting to return both of said pistons to their the other piston and so provide an abutment for mechanically transmitting force from the master piston to the floating piston, Vonly when the .maximum allowable reductionv has taken place in the working space between the two pistons,

an annular groove formed in the floating piston, Y

and a stop provided on the cylinder barrel engaging said groove for the purpose of limiting the movement of said oating piston and determining its inoperative position.

' GEOFFREY VAN VESTRAUT.

FRANK GORDON PARNELL. l 

